In the 1980s, fossil record research showed a curious cycle: Every 27 million years, Earth hosted a mass extinction. Some scientists suggested that a dim star dubbed Nemesis was in a deadly dance with our sun, periodically kicking comets out of the distant Oort Cloud to shower our planet with destruction. Morbidly fascinating as it may be, the authors of a new study argue that this “death star” theory doesn’t hold up.

The cyclical extinctions do make a solid pattern, say Adrian Melott of the University of Kansas and Richard Bambach of Smithsonian Institution Museum of Natural History, whose paper is available through arXiv.org. The two have gone back in the record to 500 million years ago, further than any other researchers, and have confirmed the 27 million year cycle at a 99 percent confidence.

According to Bambach, there’s no doubt at all that every 27 million years-odd, huge numbers of species suddenly become extinct. He says this is confirmed by “two modern, greatly improved paleontological datasets of fossil biodiversity” and that “an excess of extinction events are associated with this periodicity at 99% confidence”. This regular mass slaughter has apparently taken place around 18 times, back into the remote past of half a billion years ago. [The Register]

The problem, Nemesis fans, is that the cycle is too precise, the researchers say. If these extinctions result from a dance between our sun and Nemesis, the researchers note, the period of these mass extinctions would change as other stars buffeted the pair and changed the courses of Nemesis’s orbit around the sun.

But the data indicates that the extinctions occur every 27 million years, as regular as clockwork. “Fossil data, which motivated the idea of Nemesis, now militate against it,” say Melott and Bambuch.That means something else must be responsible. It’s not easy to imagine a process in our chaotic interstellar environment that could have such a regular heart beat; perhaps the answer is closer to home. [Technology Review]

Some scientists say that the sharply-defined periodicity isn’t enough to rule out Nemesis. Richard Muller, an author of the original Nemesis paper, told Wired.comthat there is still hope for a dark star.

“I would agree with most of what he says, but I think he is overestimating the accuracy of the geologic timescale,” he said. The geological record gives only an approximate sense of when major extinctions happened. “You get them in the right order, but it’s really difficult to get an actual date,” he said. In light of that uncertainty, “I would say the Nemesis hypothesis is still alive.” [Wired]

Luckily, given the precision of this death cycle, we can count on having time (i.e. 16 million years) to settle the debate.

There is a smidgeon of good news. The last extinction event in this chain happened 11 million years ago so, in theory at least, we have plenty of time to work out where the next catastrophe is coming from. [Technology Review]

This is the second comment on this comment string that is a non-comment.

Albert Bakker

If this is a non-story to you then you must know the definitive explanation. I don’t but I wouldn’t mind becoming informed with the latest insights.

http://www.TechyDad.com/ TechyDad

My memory is a bit clouded with pain at the moment (stress-induced muscle spasms… completely unrelated to any celestial Nemesis), but didn’t Death From The Skies (by Phil Plait) include a theory concerning the cause of these extinctions. IIRC, it was that our solar system moved up and down as it orbited the center of the Milky Way. When it rose above the galactic plane (around once every 27 million years), it would be exposed to more radiation which would result in mass extinctions on Earth.

EDIT: That’ll teach me to double-check what blog I’m reading…. I followed a link by BadAstronomer and just assumed this was a blog post by him. Bad TechyDad, making assumptions like that!

http://twitter.com/hawker101 Brian G

And here I was thinking it was 2000 years before a possibility of Nemesis appearing.

If it isn’t Nemesis, or a Death Star event, or an external cause of the deaths could it be something so simple as to be evading scientists? Could life itself have a DNA re-start button or effect?

My theory being, and forgive me if this has already been theorized elsewhere but I haven’t read this anywhere else yet, DNA can mutate only so many different ways before diversity in DNA stagnates. This stagnation causes issues similiar to inbreeding as DNA combining that are identical or very very similar cause severe mutation and a weaker organism. if this happens on a mass scale, say every 27 million years or so, life would have to re-set itself.

I know there really is no evidence to suggest this and I admit it’s a shot in the dark, but is it plausible? The Nemisis idea, to me anyhow, is more science fiction and far fetched.

#13 – I gather you refer to “genetic” or “molecular clocks.” If your basic assumption is true wouldn’t you expect for example different periodicities for smaller and larger genomes? Why would you then expect to find any discernible periodicity in biodiversity at all? Why would you think a strand of DNA can only mutate a certain number of times? Does it have a memory not to repeat itself at those loci? Why would that be bad if it is either an indifferent or beneficiary mutation? If much diversifying from beneficiary mutations is not a good idea for most individuals, would maximal diversity in DNA nevertheless be always the best survival strategy? Why would any of it lead to a fairly precise 27MA pattern of extinction events?

Furthermore the Nemesis hypothesis is not at all science fiction or particularly far fetched. Extremely long periodic events (repeating) with very accurate regularity is strongly suggestive of a causal relation (maybe indirect) of a celestial nature. The hypothesis might be true or untrue, probably the latter, but it is very serious.

HistoryTrekker

Didn’t Glaciologist Lonnie Thompson report evidence of a mass extinction about 5,200 years ago? And haven’t we heard much on the subject of the great 10000 B.C. extinction event in North America? In the case of the latter catastrophe, several books blame a cosmic disaster with a purported periodicity. That’s why it seems strange to find scientists debating 27 million year cycles when there are more pressing matters before us – like the day after tomorrow. If you’re interested, there are lots of links and analysis pertaining to this on the TheCityEdition.com 2012 pages.

I’ve read that the dinos reigned for 100 million years before their extinction. If this is correct then how can mass extinction be proclaimed a 27 million year cycle? Did they just survive the first three or four or did something change in the solar system? I’m not sure that our dating methods could be accurate over that amount of time considering the insignificant span compared by current science to determine these eras.